The government of the Solomon Islands has banned its own police chief from returning to the islands.

Shane Castles, an Australian citizen, was appointed police chief in 2005, though he is currently on leave.

He has been caught up in a mounting political row between Australia and the Solomons over a controversial sex case.

In a statement on Wednesday, Solomons Immigration Minister Patteson Oti said he had declared Shane Castles an "undesirable immigrant".

"The Solomon Islands government firmly believes Mr Castles' return and continued presence here is considered prejudicial to the peace, defence, public safety, public morality, security and good governance of the Solomon Islands," the statement said, according to Australian media reports.

The row stems from the involvement of the Solomon Islands and Papua New Guinea in the case of a fugitive Australian lawyer, Julian Moti, who is wanted on child abuse charges and who is now in the Solomons.

Canberra has asked the Solomon Islands to extradite Mr Moti to face charges.

But Mr Moti is a close friend of the Solomons Prime Minister Manasseh Sogavare, who appointed him attorney-general.

The Solomons government, which receives millions of dollars in Australian assistance, has said the extradition request is politically motivated.

Mr Sogavare was angered by a police raid on his offices in October, when police were looking for evidence into Mr Moti's escape from Papua New Guinea in October.

In September, Mr Sogavare expelled Australia's most senior diplomat from the islands, accusing him of interfering in the country's domestic affairs.